1. Field
The invention is in the field of apparatus that utilizes downhole fluid pressure in gas and oil wells to lift oil or other liquids to the surface in place of pumping.
2. State of the Art
So-called "rabbits" or "plunger lifts" are customarily employed in the relatively small diameter strings of tubing normally placed in relatively large diameter well casings for production purposes. These lifts are in the form of piston-like bodies that descend through any liquid in the tubing by free fall under the influence of gravity and that push such liquid upwardly when downhole gas pressure raises the piston in such tubing. U.S. Pat. No. 2,970,547 of Feb. 7, 1961 to E. D. McMurray shows such a lift. More recently, a gas-powered swabbing device has been developed to somewhat similarly raise oil or other liquids within the well casing itself under the control of differential pressures within such well casing, see U.S. Pat. No. 4,070,134 issued Jan. 24, 1978 to William Dwight Gramling.